Any idea how I can fix this?

With Shadows

Without Shadows

Obviously, I'm trying to get rid of that "dirty" effect.

Properties for the Main Light

The main light is the only shadow casting light in the scene. There are only two other lights, infinite lights, just for fill.
I've tried messing with the shadow min bias and blur radius, to no good effect.

Here are the render settings, in case that's of any help.

To be honest I really can't tell that much difference.  Anyway, have you
tried turning off cast shadows in the properties window of the hair itself?
Could you show us a screen shot of the hair's properties window?
Also, is it important that the hair cast a shadow onto your background?
Because then this idea might not look right unless you want to add
a shadow of the hair in the background in post work.

Maybe I'm just being a picky perfectionist, but the smudges really annoys me. ;)

I just rendered a small portion, but the smudge is all over the hair.

I'd really like to keep the shadows turned on in the hair. Since I'm trying for a somewhat dramatic scene (bright lights and dark shadows, etc), adding it in post work will be a huge pain.

Hair properties

Increasing the size of your shadow maps might help.

Quote - Increasing the size of your shadow maps might help.

Raytraced shadows don't use the map size setting.

Thanks for the reply though. ;)

I can see the difference, but I dunno if there's an easy fix. maybe displacement .001 or .01 or something. normals forward etc.

Quote - I can see the difference, but I dunno if there's an easy fix. maybe displacement .001 or .01 or something. normals forward etc.

It doesn't really look like a displacement or normals problem.  Otherwise those would show
up in the unshadowed version too.
Try enabling texture filtering in your render settings. Everybody says to turn it off,
but that's because it is a resource hog.
But some hair actually looks better with it on if you are willing to spend the extra rendering
time.  And you say you are a perfectionist and do want a better looking image.

Yeah, I tried texture filtering, no improvement at all.
It's just a raytracing/shadow min bias issue, thanks to the close layers in the hair.

Probably nothing to be done about it in poser. I hate having to import the scene to another app, but I guess it needs to be done.

Thanks for the input, all!

My understanding of the "Shadow Min Bias" is this that when testing to see if one polygon shadows another, if the points being tested are within that distance, ignore it.

Theoretically, therefore, you should be able to raise the Shadow Min Bias and eventually the various polygons in the hair that are really close will not shadow each other.

You said you tried "messing" with the shadow min bias - how did you "mess" with it? If your Poser units are inches, then you are allowing shadows within .2 inches there. Try 1 inch. But check your units first.